Once upon a time... Surfboards are made of very soft sculpted foam covered with fiberglass and epoxy or other resin. They are quite stiff in bending mode but can be fragile in localized compression (aka dings).

Ok, getting closer to having a RatShackFoamcore playing. Found some extra time and got some extra bracing put in, a second layer for the baffle speaker wire and stuffing, then glued on the other side. Waiting for glue to dry sucks.